1. Field of the Invention
The present invention relates to a dispenser for discharging a liquid material which is suitably used for a liquid crystal drip injection method, for example.
2. Description of the Related Art
A liquid crystal display device is composed of a pair of substrates and a liquid crystal inserted between the substrates. For example, one substrate is a TFT substrate on which TFTs are formed, and the other substrate is a color filter substrate on which a color filter is formed. On one substrate, an annular seal made of a light curable sealing agent is formed, and the annular seal is cured when it is irradiated with ultraviolet rays after the pair of substrates are bonded to each other. Liquid crystal is inserted into a region surrounded by the annular seal.
In the conventional method of manufacturing a liquid crystal display device, an injection hole is provided in the annular seal. After a pair of substrates are bonded to each other, the liquid crystal is injected from the injection hole provided in the annular seal in a vacuum chamber. After that, the injection hole provided in the annular seal is closed, and a liquid crystal panel composed of the pair of substrates is taken out from the vacuum chamber.
A method of manufacturing a liquid crystal display device, which is called a drip injection method, has been recently proposed (refer to Japanese Unexamined Patent Publication (Kokai) No. 2002-229044, for example). According to the drip injection method, an annular seal is formed on one of the substrates, and droplets of the liquid crystal are dripped in the annular seal. Then, the pair of substrates are bonded to each other in a vacuum chamber. According to the drip injection method, the manufacturing process can be simplified, and the manufacturing cost of a liquid crystal display device can be lowered.
In the drip injection method, in order to drip the liquid crystal onto the substrate, a dispenser for discharging a liquid material is used. The dispenser for discharging a liquid material includes a syringe having a nozzle at one end, and a plunger engaged in the syringe from the other end of the syringe. When the plunger is advanced in the syringe, droplets of the liquid crystal are ejected from the nozzle.
In the drip injection method used for manufacturing a liquid crystal display device, it is necessary to uniformly and stably discharge a small quantity of the liquid crystal from the dispenser. When the quantity of the liquid crystal discharged from the dispenser fluctuates, the thickness of a liquid crystal cell fluctuates and the quality of the display is deteriorated, and further bubbles (a vacuum layer) are generated and mixed in the liquid crystal. When bubbles and foreign objects are mixed in the liquid crystal in the syringe, the cell thickness locally fluctuates and further the liquid crystal is polluted. In order to avoid the occurrence of the above problems, it is necessary to supply a predetermined quantity of liquid crystal into the syringe without causing bubbles in the liquid crystal. It is also necessary to discharge a predetermined quantity of liquid crystal from the syringe each injection time without causing bubbles in the liquid crystals.
Not only in the dispenser for discharging a liquid material, which is used for the drip injection method of manufacturing a liquid crystal display device, but also in the syringe of the dispenser for discharging a liquid material, which is used for discharging another liquid material, when a quantity of a supplied liquid material becomes unstable, a quantity of a discharged liquid material also becomes unstable. Therefore, it is impossible to supply and discharge the liquid material stably. In the case where foreign objects are mixed in the liquid material or the liquid material itself is polluted, various problems may be caused depending on the use.